Build Thread K-Slot Rear Loaded Horn for Tangband W8-1772

[freddi]

from Zobsky's two double bass reflex cabinet pictures in Bob Brines' thread it looks like there's a compact and practical solution for some 1772 users and that a sweet spot may be around 1 cubic foot/60Hz tuning. Maybe Zobsky will split this thread or start a new one. I'd like to know the dimensions of the DBR boxes and their duct size. All 3 ducts are identical in George Augspurger's classic DBR and their chamber ratios 2:1.

 

[Godzilla]

DDHughes that's cool!

 

[yyyrik]

Hi, Zobsky. Can share the detailed plan RCA Fan's K-slot?

 

[yyyrik]

profyurik@amik.ru

 

[freddi]

here's Bill Woods page Acoustic Horn - Backload K-Horn
here's the aperture detail I saved http://img81.imageshack.us/img81/3363/al3hb9.gif

I believe it needs speakers ~ like 206-> Lowther - (I've not heard it)

 

[yyyrik]

It seems that drawing right?

 

[tomlang]

Any updates, particularly from zobsky, on this?

 

[freddi]

If (can't tell without measurements) this blh performed as predicted by AJ-Horn with 1772, it would have had a peak then dip. The same model and input looked good with FE206EN. A real Karlson may be good for 1772.

-lost AJ-Horn years ago = `$120 - ouch - the input window is the same as Bill Woods used

An externally hosted image should be here but it was not working when we last tested it.

 

[xrk971]

Sim with W8-1772 in Akabak

I just completed my model of the K-slot loaded RCA Fan back loaded horn speaker. Here is the sim with the TB W8-1772. This speaker doesn't have the best bass gain - and as a result cab benefit from 1.5mH+6ohm BSC compensation to tame the HF from this driver. The results qualitatively resemble the AJ Horn results above from the impedance plot and SPL vs Freq as the notches sort of line up.

SPL vs Freq no BSC

Impedance

Cone Excursion

SPL vs Freq with BSC

 

[xrk971]

FE166E Sim

This morning, I replaced one of my TB-1772 with my 6.5" fostex FE 166E.

Running test tones,
1. Generally speaking, this fostex isn't as efficient above 100 Hz or so.
2. At some point around or below 100 Hz, the fostex is significantly more efficient (I really need to get some measurements going).
3. Additionally with the fostex, low frequency response was extended down to the mid - late 30 Hz area.

In short, the tangband has more midbass, but the fostex seems to have lower bass and better bass definition and extension. I'd bet this is because the stronger magnet is better able to drive the horn air mass.

Here is the Freq Response with the FE206E - consistent with observations above. The Fostex is able to produce 94.4 dB at 40 Hz and 88.7 dB at 35 Hz. However, it has a 99 dB peak at 82 Hz that could be problematic.

 

[freddi]

pretty cool - how would it look with fe206en?

 

[xrk971]

FE206EN

pretty cool - how would it look with fe206en?

Your wish is but my command... 🙂

 

[freddi]

thank you very much - - what benefits might there be to this blh's Fulmer slot vs a square/rectangular mouth terminus? did the aperture require as many ducts/etc. as your k15 model? - its interesting to see the off axis prediction.

 

[IG81]

Can you check it with FF225WK for kicks? It might just work if driven by a high-damping amp. The old FF225K would have been better IMO.

IG

 

[xrk971]

IG,

Here is the FF225K

and FF225WK.

I think I like the smoother response of the WK better - although the K has a little more punch at 40 Hz.

 

[freddi]

would the original Fulmer article cabinet work without a large hole in its response? - it appeared to have almost a straight cross-section - it would be a nice size to put in corners.

according to the drawing, the slotted pipe cross-section is 8.5x9.5"

http://img451.imageshack.us/img451/8349/fuld3px.jpg

just in case a reader isn't familiar with prior art

An externally hosted image should be here but it was not working when we last tested it.

An externally hosted image should be here but it was not working when we last tested it.

 

[xrk971]

thank you very much - - what benefits might there be to this blh's Fulmer slot vs a square/rectangular mouth terminus? did the aperture require as many ducts/etc. as your k15 model? - its interesting to see the off axis prediction.

Freddi,
I think you will be pleased to learn that the K15 with its driver located behind the Karlson aperture performs better than the K-slot BLH at 1 kHz (not surprising really as with the BLH mostly it is direct radiation from the driver face, whereas with the K15, it is all funneled through the slot as an acoustic lens). Below are polar directivity plots at 100 Hz, 200 Hz, 1000 Hz at 3 meters for the Beta 10CX. I used this driver because I know it works well in a K15 cabinet already. From the plots I would day that there is a 40 deg or so cone of uniformity with the BLH and about 80 deg with the K15 before lobing becomes a significant issue. These are for sims with the speaker cabinet 48 in away from a back wall.

K15 Polar directivity

K-slot BLH Polar directivity

 

[freddi]

thanks - we can see that Karlson is vindicated on the issue of dispersion (at least in the mids) - would the factory Karlson 12 essentially scale in dispersion performance? does it matter much in dispersion characteristics with K15 whether the speaker is a 10" or a 15"? 1772 should work in a regular K - I think K12 could have had a slightly smaller rear chamber for 1772 (?)

 

[Greg B]

'Fulmer slots' are fairly effective in smoothing response in a traditional end loaded TL. Offsetting the driver from the end is somewhat more effective. If you do both -- smoother than a parked Caddy.

As the Woods K-horn is an end loaded conical pipe IIRC, I'd imagine the slot helps even out the FR.

 

[kenpeter]

Any updates, particularly from zobsky, on this?

RCAFan fulmer horn K wannabe thing???
I heard it, and no matter what we tried
to damp with pillows, it was like a tomb...

This was no Karlson, despite appearance.
Also a failure as a horn. Just a huge weird
shaped cavity behind a huge weird shape
hole, and sounded exactly that...

I believe a Karlson should pinch down the
internal cross section as the slot expands.
Especially if its to be the mouth of a horn.

---

Zobsky built himself another Ripole, only
this time with a large baffle. So much to
my surprise, actually works as intended.
Sorry, no K here. I think this time around
he was inspired by Pass' slot loaded baffle.

Was kinda rolling my eyes as I helped him
wire the damn thing. But there was nothing
to complain in the result. it sounded great!
At least where I was, directly in front of it...

Zob, sitting off to the side, seemed to be in
some kind of a nul, and wasn't getting the
full experience. He was working a miniDSP,
and leashed by the cord length of his laptop.

---

Only shame that evening was the beer
I had made. Supposed to be a brown ale
or maybe a stout. Instant coffee in bud
lite gone flat. Wasn't gross, but it wasn't
anything I was gonna drink two of...